The bikes I have are mostly 70’s machines and if they came with 27” wheels , they will probably stay that way as long as I can buy Pasela tires. I have one bike that I have gone back and forth with and the side pull brakes allow enough adjustment for both 27” and 700c. It is back to 27” for now. I use SunTour or Regina freewheels , 5 or 6 speed with mostly Campagnolo Record high flange hubs. With the SRAM 8 speed chain , the shifting is nice with no slipping at all .